Electrical apparatus



Feb. 8, 1944. F. J. VOGEL ELECTRICAL APPARATUS Filed Dec. 18, 1941 INVENTOR fiedf/a 'e/ k414i? ATTORNEY #615 C00 cen/raf/on Pain 1 5 5 WETNESSES: ay

Patented Feb. 8, 1944 UNITED STATES PATENT OFFICE ELECTRICAL APPARATUS Fred J. Vogel, Sharon, Pa., assignor to Westinghouse Electric & Manufacturing Company,

East Pittsburgh, Pa., a

sylvania corporation of Penn- 8 Claims.

My invention relates to electrical induction apparatus, such as transformers, and particularly to the insulation of tap changing switches from the casing of such apparatus.

In electrical transformers for changing the voltage ratio between primary and secondary circuits, it is frequently customary to provide tap changing apparatus including a tap changing switch for changing circuit connections of a plurality of tap conductors leading from the winding in order to vary the effective number of winding turns in one of the windings and thereby to vary the voltage ratio between the primary and secondary circuits. Tap changing apparatus of the hand operated type requires a mechanical connection of insulating material between the tap changing switch and the operating handle, which connection must be mechanically rigid and strong. A connection comprising a shaft formed of various insulating materials such as porcelain, or the material sold under the trade-mark Micarta, which is a textile material impregnated with a binder hardened under heat and pressure, has been used. This material is, however, not reliable for impulse tests or lightning strokes, or has low strength, especially when a steep front voltage wave is applied. This is particularly true if the winding taps and tap changing switch are connected near the line end of the winding.

The unreliability of such prior art uses of the insulating shaft is due to too great a 'concentration of electrostatic stresses along the surface of the material. This concentration of stress may be reduced by providing shielding means on the insulating shaft.

It is an object of the invention to provide a tap changing device including an operating mechanism connected between the tap changing switch structure and an operating handle having high mechanical strength and formed of material having low dielectric properties so shielded'as to provide a structure of high dielectric quality.

Other objects and advantages of the invention will be apparent from the following description of certain preferred embodiments thereof, reference being had to the accompanying drawing, in which:

Figure 1 is an elevational view partly in section of a transformer having a tap changing device organized in accordance with the invention,

Fig. 2 is a diagrammatic illustration of one arrangement of the transformer circuits employing a tap changing switch,

Fig. 3 is an enlarged vertical sectional view through a part of the structure shown in Fig. "1,

Fig. 4 is a horizontal sectional view taken on lines IV-IV of Fig. 3, and

Fig. 5 is a vertical sectional view of structure comprising a modified form of the invention.

Referring to the drawing and particularly to Fig. 1 thereof, the numeral I identifies a metal tank or casing for an electrical apparatus comprising a magnetic circuit core structure 2 and winding 3 that are normally insulated and cooled by an insulating and cooling liquid 4. The winding terminal conductors lead to circuits exterior to the casing through bushings 5 which are shown as mounted on a cover 6 of the casing I. A tap changing switch structure is shown at l which is arranged to be operated by a handle 8 here shown above the cover 6, and from which a metal shaft 9 extends toward the tap changing switch device I and is operatively connected thereto through an insulating coupling structure II, a lower metallic shaft l2 and a universal joint I3. As shown in Fig. 2, the various switch contact members of the tap changing switch 1 may be connected through tap conductors M to selected points on winding parts l5 and I6 which together may constitute one of the transformer windings, the other winding being shown at In. It will be appreciated that the arrangement of the windings shown is purely conventional and that other arrangements may be employed such as the conventional auto-transformer winding in which the primary and secondary windings are conductively connected. It will also be appreciated that the tap conductors may be connected at other convenient points than as shown, such as near the line or high voltage end of an auto-transformer winding.

Referring particularly to Figs. 3 and 4, the coupling mechanism l I between the spaced ends of the shafts 9 and I2 is shown as comprising a disk I! of insulating material attached to the end of the metal shaft 9 and a similar disk of insulating material l8 attached to the end of the metal shaft [2, the two disks being connected by a wall or cylinder of insulating material I9 of much greater diameter than the shafts, the entire structure being attached to the shafts by means of the nuts 2| and 22 to form a rigid coupling that is mechanically strong.

It will be appreciated that the metal shaft 9 will be at ground or casing potential, and that the shaft l2 will be at a potential substantially that of the tap changer switch 1. Should a high voltage surge having a steep wave front be applied to the apparatus, such as might result from a lightning stroke or from surge testing of the apparatus, electrostatic stresses will normally build up between shafts 9 and 12 in the insulating member H. These stresses are concentrated on the insulating material adjacent to nuts 2! and 22 and also result in a weakness between the shaft I2 and other parts of the apparatus, such as the core or tank wall. In accordance with the invention, the coupling comprising disks ll, [8 and the cylindrical wall l9 are provided with shields to relieve this concentration of stress. These shields consist of metallic members 23 and 24 on the opposite sides of the insulating disk I8 and provided with a body portion and an outer annular rim portion 26 having rounded edges that are spaced outwardly from the shaft l2 and also from the disk l8. The rim 26 is supported on the outer edge of a body portion including a fiat circular part 21 positioned closely adjacent to the disk l8 and a substantially cylindrical part 28 shown as spaced from and surrounding the axis of the shaft 12 and provided with an outwardly extending rim 29 terminating in the rounded edges 25. An annular body of high specific inductive capacity material such as Fullerboard washers 3| may be provided about the cylindrical wall portions 28 for relieving the electrostatic concentration of stress that might otherwise occur at the corners resulting from the intersection of the cylindrical portion 28 with the flat disk portion 21 of the shield. The two shield structures shown on opposite sides of the insulating disk 18 are similar in construction, and, as illustrated, are positioned with their outer annular rims in spaced relation on opposite sides of the disk l8. Shields similar to 23 and 24 shown on the opposite sides of the disk 18, may also be provided on opposite sides of the disk about the end of the shaft 9, or one only of these shields may be used adjacent the spaced ends of one or both of the shafts l2 and 9 as found necessary to meet particular surge test requirements.

Referring to Fig. 5, a modified form of the invention is illustrated employing a shaft 4| of insulating material extending from the coupling 13 to the handle 9. The shaft 41 may, like the cylinder 19, be made of insulating material such as that sold under the trade-mark Micarta. Metal shields 42 are provided attached to the shaft 4! at either end thereof and they may be similar in construction to the shields 23 and 24 shown in Figs. 3 and 4, and consist essentially of an outer annular rim portion 43 having rounded outer edges carried by a body portion including a cylindrical wall 44 carried by an annular disk part 45, the inner edges of which may be provided with an inner collar portion 46 closely surrounding the shaft 4| and the drive shafts 9 or l2. An annular member 47 having high dielectric strength may be positioned about the shaft 4| within the cupshaped shield 42 fitting closely adjacent to the shaft and the disk part 45 of the body portion to relieve the stress concentration that might otherwise develop on the annular edge or point, as shown in section between the collar part i6 and the disk part 45 of the shield. This shield may be duplicated so that two such shields are provided in spaced relation along the shaft 4| as shown. It will be noted that the shields are placed below the level of the insulating liquid used in the apparatus.

It will be apparent to those skilled in the art that modifications may be made within the spirit of my invention, and I do not wish to be limited otherwise than by the scope of the appended claims.

I claim as my invention:

1. In an electrical apparatus, a metal casing, an electrical adjusting device within said casing subject to high voltage, means for operating said electrical adjusting device including a handle and a shaft of insulating material operatively connected between the device and the handle, and means for distributing the dielectric flux on the shaft comprising a metallic shield having a body portion about the shaft comprising adjoining cylindrical and flat circular surface parts and an outer annular rim having rounded edges, and an annular body of high-specific inductive capacity material about the shaft adjacent the junction between said cylindrical and circular disk surface parts for relieving the high electrostatic stress concentration.

2. In an electrical apparatus, a metal casing, an electrical adjusting device within said casing subject to high voltage, an operating mechanism for said device, said mechanism comprising an operating handle, a shaft extending inwardly from the handle toward said electrical device, a shaft extending outwardly from the electrical device toward the first named shaft, the ends of the two shafts being positioned in spaced relation to each other, and a mechanical structure for coupling the spaced ends of the two shafts comprising a disk of insulating material attached to the end of each shaft and means for mechanically connecting said disks, and means for distributing the dielectric flux adjacent the outer end of the inner shaft comprising metallic shields on opposite sides of the disk attached to the end of the shaft, said shields having fiat circular body portions closely adjacent to the disk and outer annular rounded rim portions spaced from the shaft and from the disk.

3. In an electrical apparatus, a metal casing, an electrical adjusting device within said casing subjectto high voltage, an operating mechanism for said device, said mechanism comprising an operating handle, a shaft extending inwardly from the handle toward said electrical device, a shaft extending outwardly from the electrical device toward the first named shaft, the ends of the two shafts being positioned in spaced relation to each other, and a mechanical structure of insulating material for coupling the spaced ends of the two shafts comprising a disk of insulating material attached to the end of each shaft and means for mechanically connecting said disks, and means for distributing the dielectric flux adjacent the spaced end of a shaft comprising metallic shields having body portions including fiat circular parts extending outwardly from the shaft along opposite sides of the disk, cylindrical wall parts extending from the outer edge of the circular parts away from the disk and provided at their outer edges with outwardly extending rim portions terminating in rounded annular outer edges, and an annular body of high-specific inductive capacity material about the cylindrical wall portions of the shields for relieving the high electrostatic stress concentration.

4. In an electrical apparatus, a metal casing, an electrical adjusting device within said casing subject to high voltage, an operating mechanism for said device comprising a circular shaft of insulating'material extending from said device and means for-distributing the dielectric flux on the shaft comprising a metal shield having a body portion attached to the shaft and extending outwardly from the shaft, along the shaft and about the shaft and terminating in an outer annular rim having rounded edges encircling the shaft a substantial distance along the shaft from the part of the shaft from which the body portion extends outwardly.

5. In an electrical apparatus, a metal casing, an electrical adjusting device within said casing subject to high voltage, an operating mechanism for said device comprising a circular shaft of insulating material extending from said device and means for distributing the dielectric flux on the shaft comprising a metal shield having a fiat circular body portion extending outwardly from the shaft, and continuing in a cylindrical wall about the shaft and terminating in an outer annular rim having rounded edges, and an annular member having high dielectric strength about the shaft and fitting closely to the shield within said outer cylindrical wall portion.

6. In an electrical apparatus, a metal casing, an electrical adjusting device within said casing subject to high voltage, an operating mechanism for said device, said mechanism comprising an operating handle, a shaft extending inwardly from the handle toward said electrical device; a shaft extending outwardly from the electrical device toward the first named shaft, the ends of the two shafts being positioned in spaced relation to each other, and a mechanical structure of insulating material for coupling the spaced ends of the two shafts comprising a disk of insulating material attached to the end of each shaft and means for mechanically connecting said disks, and means for distributing the dielectric flux adjacent the spaced end: of at least one of the shafts comprising a metallic shield on at least one side of the disk attached to the end of the shaft, said shield having a flat circular body portion closely adjacent to the disk and an outer annular rounded rim portion spaced from the shaft and from the disk.

7. In an electrical apparatus, a metal casing, an electrical adjusting device within said casing subject to high voltage, an operating mechanism for said device, said mechanism comprising an operating handle, a shaft extending inwardly from the handle toward said electrical device, a shaft of insulating material extending outwardly from the electrical device toward the first named shaft, the ends of the two shafts being positioned in spaced relation to each other, and a mechanical structure for coupling the spaced ends of the two shafts comprising a disk of insulating material attached to the end of each shaft and means for mechanically connecting said disks, and means for distributing the dielectric flux adjacent the disks comprising metallic shield associated with each disk and having a body portion including a fiat circular part extending outwardly from the shaft along one side of the disk, a cylindrical wall part extending from the outer edge of the circular part away-from the disk and providing its outer edges with an outwardly extending rim portion terminating in a rounded annular outer edge, and an annular body of high-specific inductive capacity material adjacent the cylindrical wall portion of the shield for relieving the high electrostatic stress concentration.

8. In an electrical apparatus, a metal casing, an electrical adjusting device within said casing subject to high voltage, an operating mechanism for said device comprising a circular shaft of insulating material extending from said device and means for distributing the dielectric flux on the shaft comprising a pair of metal shields in spaced relation with each other and each shield having a supporting body portion extending outwardly from the shaft and extending about the shaft and terminating in an outer annular rim having rounded edges, the rim portion of the shield extending about a portion of the shaft somewhat along the shaft from the inner portion of the body adjacent the shaft, the two shield members having their rim portions nearest each other and thlelir supporting portions more remote from each ot er.

FRED J. VOGEL. 

